Recently, plasma display panels (PDPs), field emission display (FED) devices, and thin film transistor-liquid crystal display (TFT-LCD) devices have been developed as flat-panel display devices used for notebook computers, televisions (TVs), or mobile phones that require a thin design, a small size, and low power consumption. From among the flat-panel display devices, the LCD devices having good color reproduction and a thin design have been most actively studied.
Since the PDPs and the FED devices, from among the flat-panel display devices, may emit light by themselves whereas the LCD devices may not emit light by themselves, the LCD devices may display images by emitting light by using backlight units that are auxiliary light sources. In order to meet the demand that backlight units uniformly emit light to entire surfaces, the backlight units have edge-type or direct-type surface light source structures.